Copy protection is important technology for any digital transmission. There are several technology aspects for achieving copy protection (e.g., content scrambling, key exchange, key revocation, watermarking, etc.). Content scrambling is widely used in DVD playback to protect original content. Modern scrambling techniques employ large keys for scrambling. Modern scrambling techniques also have unique keys for each product. For security, the unique keys cannot be in the open (i.e., directly readable). Conventional techniques scramble the keys.
Referring to FIG. 1, a block diagram illustrating a conventional copy protection scheme 10 is shown. Because of the uniqueness and large length of the keys, scrambling is implemented in software. A general purpose processor (CPU) 12 with block cipher instructions executes a software process 14 which is configured to descramble scrambled content 16 using keys 18. The processor then presents the content in the clear (i.e., unscrambled).
However software cryptographic algorithms are vulnerable to hacking. In the conventional system, the software process 14 and the keys 18 are stored separately. Typically, hackers target the software implementation to reverse engineer the software process 14. Reverse engineering is done by single stepping or inserting break points into the code for the software process 14.
It would be desirable to have a method for preventing reverse engineering of software cryptographic processes.